The invention relates to a multi-cylinder internal combustion engine with an exhaust-gas turbocharger and with at least two separate exhaust-gas lines to the turbine of the exhaust-gas turbocharger which are assigned to different cylinders or cylinder groups, and which can be joined ahead of the turbine or maintained separated depending on the operating condition of the engine.
In the case of supercharged internal combustion engines, in particular engines with an unfavourable ignition sequence, such as, for example, 8- or 5-cylinder engines, the charge exchange can be improved by feeding the turbine with separate exhaust-gas streams from different cylinders or cylinder groups. With pulse charging, in which, where appropriate, the exhaust gases from each cylinder are supplied individually to the turbine, interaction of the cylinders with one another is reduced or avoided. Some of the otherwise unusable expansion energy of the cylinders can be recovered by means of pulsed charging, whereby the transport of energy to the turbine is greatly improved. Particularly in the lower to medium load and speed range of the internal combustion engine, the delivery of air to the engine is assisted by the increased turbine power and the correspondingly increased compressor output of the exhaust-gas turbocharger. However, in the upper load range, for example above the medium speed of the internal combustion engine, conventional turbine designs will give rise, in the case of pulsed charging, to overcharging of the engine.
DE 32 00 521 C2 proposes an arrangement which provides two parallel exhaust-gas lines for conducting the exhaust gases to the turbine. The exhaust-gas lines have a connection upstream of the turbine and can be fluidically connected or they can be kept separated depending on the position of an actuator. The actuator is designed as a rotatable intermediate wall of the turbine inlet ports, having an axis of rotation coinciding with the turbine axis. The rotatable intermediate wall is controlled by a control unit and is brought into one of the end positions, as required, depending on the operating load. For pulsed charging in the lower partial load range, the exhaust-gas lines are separated, but they are in communication with one another in the other end position of the intermediate wall.
In the known device, in which the rotatable intermediate wall between two adjacent ports controls the fluidic communication or separation between the exhaust-gas streams from the cylinders to the turbine, effective pulsed charging and the change-over between the two charging methods available can not be achieved for multicylinder internal combustion engines, or only with a high structural outlay. Each pair of exhaust-gas lines has to have its own actuator, and the actuating movements of the various actuators must be synchronized.
It is the object of the present invention to provide on internal combustion engine, which, with a low structural outlay, permits communication between, or separation of, the exhaust-gas lines upstream of the turbine, as required.